[clang] [clang-tools-extra] Remove `StringLiteral` in favor of `StringRef` (PR #122366)

[David Blaikie via cfe-commits]

dwblaikie wrote:

> Anyway, my main point was that there are people who care about performance on Windows, so please don't treat it as a second-class citizen.

Yeah, I don't want to treat folks on Windows as second class citizens by any means - but I wouldn't mind/hope we can treat folks who care about performance but don't build their performance-critical binaries with clang, on platforms clang supports, as a lower priority. Yeah, don't make the build unusable when built without clang, but I don't think/hope we don't need to try too hard to get every ounce of performance out of every host compiler when/where that performance can be obtained with a bootstrap. Helps avoid us bending over backwards for compilers we can't fix, etc. Compared to making better tradeoffs between source workarounds and compiler improvements wholely within our control.

https://github.com/llvm/llvm-project/pull/122366